Welding materials for aluminum-coated steel

ABSTRACT

In welding materials, such as a composite electrode enclosing a flux within a tubular hoop, a combination of a solid electrode and a flux, a core electrode coated with a flux and the like, for welding aluminum-coated steel comprising on weight basis less than 1.5% of Si less than 1.0% of Mn, and 2 to 15% of CaF 2  and 15 to 50% of a mixture of oxides having a basicity ranging from 1.0 to 12.5, the balance being substantially Fe.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to welding materials for aluminium-coated steel, particularly for steel which has been spray-coated with molten aluminium.

The term "welding materials" as referred to herein means generically a combination of materials comprising slag forming agents, deoxidizers, organic materials, steel and the like contained in a flux, welding electrode and the like.

Because of its excellent corrosion and thermal resistances, aluminium-coated steel has been employed for various purposes. There has been, however, available no special welding materials for aluminium-coated steel, so that conventional welding materials have been unavoidably employed for welding the same.

When aluminium-coated steel is welded by employing such conventional welding materials for steel, the affinity of aluminium for the oxygen dissolved in the weld metal is so strong that the metallic Si and Mn, including Fe-Si, Ca-Si, Fe-Mn and the like, added for the deoxidation in the welding electrode and flux are not consumed. As a result, metallic Si and Mn are dissolved excessively in the weld metal. Moreover, metallic Si and Mn are also formed by the reduction of oxides of Si and Mn such as SiO₂, CaSiO₃, Na₂ SiO₃, MnO, MnO₂, MnSiO₃, MnCO₃ and the like which are, contained in the flux as slag forming agents. The Si and Mn are again dissolved in the weld metal thereby increasing the crack sensibility by increasing the hardenability and reducing markedly the notch toughness through the formation of lath-like bainitic structures.

It is thus an object of this invention in view of such a problem to provide welding materials for aluminium-coated steel which are capable of improving the properties of the weld metal by controlling the Si- and Mn-contents in the weld metal to within preferred ranges without deteriorating the welding operability.

According to this invention, there are provided welding materials which are comprised of a flux and a welding electrode, such as a composite electrode enclosing a flux within a tubular hoop, a core wire electrode coated with a flux for arc welding and the like. These materials comprise on weight basis less than 1.5% of Si and/or less than 1.0% of Mn, and 2 to 15% of CaF₂ and 15 to 50% of a mixture of oxides which have a basicity ranging from 1.0 to 12.5, the balance being essentially Fe. The term "basicity" as referred to herein means a ratio by weight of the amount(s) of CaO and/or MgO with respect to SiO₂ and may be represented by the following formula:

    (CaO + MgO)/SiO.sub.2

wherein CaO, MgO and SiO₂ are the amounts by weight which are formed finally by decomposition during welding.

Such limitations are a result of the following facts: (1) When the Si-content exceeds 1.5% and the Mn-content exceeds 1.0%, the weld metal will be deteriorated in notch toughness. (2) If the amount of CaF₂ is less than 2%, the slag formed during the welding will be excessively fluid and if the amount of CaF₂ exceeds 15%, the fluidity of the slag will be excessively poor, both causing the welding operation to be inconvenient. (3) If the oxides are contained in an amount of less than 15%, the slag will be formed to a lesser extent to enhance the cooling rate of the weld metal thereby causing a reduction in toughness of the weld metal and if the oxide content exceeds 50%, the welding operation will be difficult to perform. (4) If the basicity is less than 1.0%, the weld metal will be deteriorated in toughness and if it exceeds 12.5%, the welding workability will be deteriorated.

This invention will be illustrated further by way of the following examples.

EXAMPLE 1

The welding materials according to this invention were compared with ones used conventionally for welding of aluminium-coated steel plates as shown in Table 3, by employing welding materials shown in Table 1 under the welding conditions as shown in Table 2. Table 4 provides the test results of weld metals.

                                      Table 1                                      __________________________________________________________________________     Composition of welding materials for                                           submerged arc welding, % by weight                                                                                               Welding   Basi-                       Flux of sintering type                   electrode city               Run No     Si  Mn CaO MgO CoF.sub.2                                                                         SiO.sub.2                                                                          Al.sub.2 O.sub.3                                                                   TiO.sub.2                                                                         Na.sub.3 O                                                                        ZrO.sub.2                                                                         CeF Si  Mn Fe                    __________________________________________________________________________                                                              Bala-                 Present  A --  -- 4.5 15  5.0                                                                               11.5                                                                               2.5 4.5                                                                               2.0                                                                               0.5                                                                               --  tr  8.35                                                                              nce                                                                               1.7                Invention                                                                               B  0.15                                                                              -- 5.0 16  4.0                                                                               5.0 1.5 4.5                                                                               2.3                                                                               4.5                                                                               9.0 tr  0.15                                                                              "  4.2                         C --  -- 5.0 15  4.5                                                                               4.0 2.5 4.5                                                                               2.0                                                                               4.5                                                                               10.0                                                                               0.15                                                                               0.35                                                                              "  5.0                         D 0.1 0.2                                                                               7.0 15  4.0                                                                               3.5 4.5 4.5                                                                               2.7                                                                               4.5                                                                               4.0 tr  0.15                                                                              "  63                          E  0.05                                                                              0.15                                                                              5.0 15  4.0                                                                               8.5 2.5 4.5                                                                               1.8                                                                               4.5                                                                               4.0 tr  0.15                                                                              "  2.4                __________________________________________________________________________     Conventio-                                                                              F 0.3 0.85                                                                              6.0 13  3.5                                                                               17.5                                                                               4.5 2.0                                                                               2.4                                                                               -- --  0.015                                                                              0.2                                                                               "  1.1                nal proce-                                                                              G  0.25                                                                              0.75                                                                              12.0                                                                               5.5 2.5                                                                               19  4.5 4.0                                                                               1.5                                                                               -- --  0.015                                                                              0.3                                                                               "  0.9                dure     H 0.6 1.75                                                                              7.5 14.5                                                                               3.5                                                                               13.5                                                                               2.5 4.0                                                                               2.2                                                                               -- --  tr  0.15                                                                              "  1.6                         I 0.2 0.6                                                                               6.0 14  4.5                                                                               13.5                                                                               2.5 3.5                                                                               1.6                                                                               3.5                                                                               --  tr  0.15                                                                              "                     __________________________________________________________________________                                                                 1.5                 Note : The welding electrodes in Run Nos. A and C were composite               electrodes and those in other runs were solid electrodes.                

                  Table 2                                                          ______________________________________                                         Welding conditions in each pass for double welding                                          Finishing welding                                                                         Backing welding                                        Welding current, Amp.                                                                         900          750                                                Arc voltage, V 40                                                              welding speed, cm/min.                                                                        40                                                              ______________________________________                                    

                  Table 3                                                          ______________________________________                                         Steel plate to be welded                                                       Thickness: 12mm                                                                Grade: 50 Kg/mm.sup.2 high strength steel                                      Composition                                                                               C       Si      Mn    P      S                                               0.15  0.30    0.99    0.017   0.015                                   ______________________________________                                          Note: Film thickness of coated aluminium: 100 microns                    

                                      Table 4                                      __________________________________________________________________________     Test results of weld metal                                                     Composition of weld metal                                                                       Impact value of weld metal, Kg-m                              Run No.                                                                            Si  Mn  Al   vE.sub.20                                                                            vEo   vE-20                                             __________________________________________________________________________     A   0.25                                                                               0.98                                                                               0.042                                                                               15.7  15.0  10.1                                              B   0.27                                                                               0.95                                                                               0.045                                                                               12.3  8.7   8.0                                               C   0.22                                                                               0.86                                                                               0.043                                                                               15.9  15.7  15.1                                              D   0.29                                                                               1.02                                                                               0.042                                                                               15.3  10.3  6.1                                               E   0.31                                                                               1.01                                                                               0.050                                                                               13.3  8.4   5.5                                               F   0.52                                                                               1.50                                                                               0.118                                                                               6.4   3.6   1.9                                               G   0.43                                                                               1.35                                                                               0.073                                                                               4.0   2.7   1.4                                               H   0.55                                                                               1.56                                                                               0.130                                                                               4.2   3.0   1.5                                               I   0.46                                                                               1.32                                                                               0.087                                                                               6.8   3.5   2.2                                               __________________________________________________________________________

As shown in the test results in this example, when the Si- and Mn-contents are decreased in the welding materials, it can be seen that the weld metal obtained has a better toughness.

EXAMPLE 2

When steel plates spray-coated with molten aluminium, as shown in Table 5, were fillet welded by employing a covered electrode having a composition as shown in Table 6, the test results were as shown in Table 7.

                                      Table 5                                      __________________________________________________________________________     Chemical composition of base metal, % by weight                                                                 Film thickness                                                C  Si Mn P   S   of Al, microns                                Steel plate spray-coated                                                       with molten aluminium                                                                          0.14                                                                              0.40                                                                              1.29                                                                              0.023                                                                              0.010                                             having a thickness of 12 mm                                                    __________________________________________________________________________

                                      Table 6                                      __________________________________________________________________________     Composition of welding materials of arc welding                                electrode coated with a flux, % by weight                                                                    Conventional                                                                   covered electrode                                Covered electrode having a diameter of 5.0mm                                                                 of low-hydrogen                                  of this invention (Total contents in the core                                                                type having a                                    and coated flux)              diameter of 5.0mm                                No. 1     No. 2                                                                               No. 3                                                                               No. 4                                                                               No. 5                                                                               No. 6                                                                               No. 7                                       Si   1.2  1.2  0.8  0.8  1.4  2.2  2.9                                         Mn   --   --   --   0.5  --   0.5  0.6                                         CaCO.sub.3                                                                          17.7 15   18   17.7 11.4 15   15.75                                       CaF.sub. 2                                                                          6.3  9    6.6  6.3  4.5  4.8  1.5                                         MgO  0.45 0.45 0.6  0.45 0.3  0.3  --                                          ZrSiO.sub.4                                                                         0.75 0.75 0.75 0.75 0.6  --   --                                          TiO.sub.2                                                                           1.5  1.5  1.65 1.5  1.35 2.25 1.2                                         Mica 0.75 0.75 0.75 0.75 0.66 0.36 0.6                                         Sodium                                                                              0.15 0.15 0.15 0.15 0.09 0.09 0.15                                        alginate                                                                       Fe   Balance                                                                             Balance                                                                             Balance                                                                             Balance                                                                             Balance                                                                             Balance                                                                             Balance                                     Basicity                                                                            10.3 8.8  10.7 10.3 8.7  5.8  6.8                                         __________________________________________________________________________

                                      Table 7                                      __________________________________________________________________________     Test results of weld metal                                                                                           Commercially                                                                   available                                Welding electrode                                                                              Electrode of this invention                                                                          electrode                                to be tested                                                                                   No. 1                                                                              No. 2 No. 3                                                                              No. 4                                                                              No. 5                                                                              No. 6 No. 7                              __________________________________________________________________________     Chemical                                                                               C       0.10                                                                               0.11  0.12                                                                               0.10                                                                               0.11                                                                               0.12  0.12                               composition                                                                            Si      0.46                                                                               0.48  0.34                                                                               0.23                                                                               0.24                                                                               0.90  1.13                               of weld metal                                                                          Mn      0.57                                                                               0.60  0.73                                                                               1.08                                                                               0.68                                                                               1.23  1.42                                       Sol. Al 0.11                                                                               0.11  0.15                                                                               0.20                                                                               0.23                                                                               0.36  0.25                                Hardness of weld metal.sup.1)                                                                  238Hv                                                                              236Hv                                                                                238Hv                                                                              221Hv                                                                              228Hv                                                                              283Hv                                                                                328Hv                                     Tensile                                                                        strength,                                                              Cross fillet                                                                           Kg/mm   55.3                                                                               54.7  53.6                                                                               56.2                                                                               54.5                                                                               54.8  55.3                               tension test.sup.2)                                                                    Broken area                                                                            Depo.                                                                              Base metal                                                                           Depo.                                                                              Depo.                                                                              Depo.                                                                              Base metal                                                                           Base metal                         __________________________________________________________________________             Appearance                                                                             ⊚                                                                   ○                                                                             ○                                                                           ⊚                                                                   ⊚                                                                   x     x                                          of bead                                                                        Fluidity                                                                               ○                                                                           ⊚                                                                     ○                                                                           ⊚                                                                   Δ                                                                            x     x                                          of slag                                                                results Covering                                                               of weld property                                                                               ○                                                                           Δ                                                                              ○                                                                           ○                                                                           ⊚                                                                   x     x                                  metal   of slag                                                                        Peeling-off                                                                            ○                                                                           ○                                                                             ○                                                                           Δ                                                                            Δ                                                                            Δ                                                                              x                                          of slag                                                                        Overall ⊚                                                                   ○                                                                             ○                                                                           ○                                                                           ○                                                                           x     x                                          evaluation                                                             Pits and blow holes                                                                            Nil Nil   Nil Nil Nil Nil   Nil                                Cracks          Nil Nil   Nil Nil Nil Nil   occur                              __________________________________________________________________________      Note:                                                                          .sup.1) Tested according to Vickers hardness tester under a load of 10 Kg      .sup.2) Tested by the method according to JIS Z-3131                           .sup.3) Tested by the methods according to JIS Z-3002 and compared with        the results obtained by welding bare steel plate with commercially             available electrode under the following criteria:                               ⊚: Excellent                                                    ○: Same                                                                 Δ: Slightly inferior                                                     X: Inferior                                                             

EXAMPLE 3

Steel plates having the dimensions and composition as shown in Table 8 were spray-coated with molten aluminium in an average film thickness of 70 microns. The plates were then fillet welded by carbon dioxide gas arc welding. In examples of this invention and comparative examples, composite electrodes as shown in Table 9 were employed and welded under the conditions as shown in Table 10. Table 11 shows comparisons of the welding results. From these results, it can be seen that properties of the weld metals and state of welded area are superior in the use of electrodes according to this invention to conventional ones.

                  Table 8                                                          ______________________________________                                         Composition of hot rolled                                                      steel plate to be employed                                                     (thickness: 12mm)                                                              C        Si        Mn        P       S                                         ______________________________________                                         0.14     0.40      1.29      0.009   0.010                                     ______________________________________                                    

                                      Table 9                                      __________________________________________________________________________     Chemical composition of welding materials, % by weight                         Enclosed flux                 Hoop                     Basi-                           Si Mn CaCO.sub.3                                                                         CaO                                                                               CaF.sub.2                                                                         TiO.sub.2                                                                         SiO.sub.2                                                                         Others                                                                               C  Si Mn Mo P S Fe city                    __________________________________________________________________________                                                         Bala-                            1 0.1                                                                               0.5                                                                               0.4 1.2                                                                               7.2                                                                               4.6                                                                               1.0                                                                               --    0.05                                                                              <0.1                                                                              0.3                                                                               -- --                                                                               --                                                                               nce                                                                               1.4                     Composite-                                                                           2 0.3                                                                               0.6                                                                               0.4 1.2                                                                               6.5                                                                               5  1.0                                                                               --    "  "  "  -- --                                                                               --                                                                               "  1.4                     electrode                                                                            3 0.3                                                                               0.7                                                                               0.8 1.0                                                                               5.7                                                                               5  1.4                                                                               --    "  "  "  -- --                                                                               --                                                                               "  1.0                     of this                                                                              4 0.14                                                                              0.4                                                                               0.6 1.0                                                                               6.46                                                                              5  1.0                                                                               --    0.06                                                                               0.29                                                                             0.3                                                                               0.16                                                                              --                                                                               --                                                                               "  1.3                     invention                     Ni 1.34                                                5 0.14                                                                              0.4                                                                               0.4 1.0                                                                               8.52                                                                              4.6                                                                               0.8                                                                               Cr 0.4                                                                               "  "  "  "  --                                                                               --                                                                               "  1.5                                                   Ni 1.34                                                6 0.14                                                                              0.4                                                                               0.4 1.0                                                                               8.2                                                                               3.6                                                                               0.8                                                                               Cr 0.1                                                                               "  "  "  "  --                                                                               --                                                                               "  1.5                                                   Mo 0.4                                           __________________________________________________________________________     Conventi-                                                                            7 0.6                                                                               1.6                                                                               0.8 3.0                                                                               4.3                                                                               5.0                                                                               1.0                                                                               --    0.06                                                                              <0.1                                                                              0.3                                                                               -- --                                                                               --                                                                               "  3.4                     onal com-                                                                            8 0.7                                                                               1.6                                                                               0.4 1.2                                                                               3.1                                                                               8  1.6                                                                               --    "  "  "  -- --                                                                               --                                                                               "  0.9                     posite                                                                               9 0.7                                                                               1.5                                                                               1.6 1.2                                                                               6.7                                                                               1.6                                                                               3.0                                                                               --    "  "  "  -- --                                                                               --                                                                               "  0.7                     electrode                                                                      __________________________________________________________________________

                                      Table 10                                     __________________________________________________________________________     Welding conditions                                                                               Flow rate of                                                 Current                                                                             Voltage                                                                             Welding speed                                                                          shielded Co.sub.2                                                                     Welding                                               Amp  V    cm/min  liters/min.                                                                           position                                                                             Power source                                    __________________________________________________________________________     300  36˜38                                                                         37      (CO.sub.2)                                                                            Horizontal                                                                           DC, Constant Voltage,                                             25     fillet                                                                               reverse polarity                                __________________________________________________________________________

                                      Table 11                                     __________________________________________________________________________     Welding results                                                                       Composition of weld                                                                             Properties of weld                                            metal, % by weight                                                                              metal                                                  Elec-           Sol     Hardness                                                                            Blow    Appearance                                                                           Peeling-off                         trode  C  Si Mn Al Others                                                                              (Hv) holes                                                                              Cracks                                                                             of bead                                                                              of slag                             __________________________________________________________________________         1  0.09                                                                              0.28                                                                              0.9                                                                               0.24                                                                              --   203  Nil Nil Good  Good                                    2  0.10                                                                              0.31                                                                              1.08                                                                              0.25                                                                              --   235  "   "   "     "                                       3  0.11                                                                              0.33                                                                              1.30                                                                              0.28                                                                              --   248  "   "   "     "                                   Exam-                                                                          ple 4  0.10                                                                              0.38                                                                              1.35                                                                              0.26                                                                              Mo 0.15                                                                             263  "   "   "     "                                                      Ni 1.8                                                          5  0.08                                                                              0.35                                                                              1.25                                                                              0.20                                                                              Cr 0.45                                                                             281  "   "   "     "                                                      Mo 0.15                                                                        Ni 1.8                                                          6  0.08                                                                              0.37                                                                              1.20                                                                              0.23                                                                              Cr 0.8                                                                              294  "   "   "     "                                                      Mo 0.6                                                      __________________________________________________________________________     Comp-                                                                              7  0.09                                                                              0.55                                                                              1.49                                                                              0.15    284  "   "   Poor  "                                   ara-                                                                           tive                                                                               8  0.10                                                                              0.55                                                                              1.48                                                                              0.20    274  Occur                                                                              "   "     Good                                exam-                                                                          ple 9  0.12                                                                              0.59                                                                              1.45                                                                              0.18    283  Nil "   "     "                                   __________________________________________________________________________ 

What we claim is:
 1. Welding materials for aluminium-coated steel comprising on weight basis less than 1.5% of Si, and less than 1.0% of Mn, 2 to 15% of CaF₂, and 15 to 50% of a mixture of oxides having a basicity ranging from 1.0 to 12.5, the balance being essentially Fe.
 2. Welding materials for submerged arc welding according to claim 1 comprising on weight basis 0.1 to 0.3% of Si and 0.3 to 0.8% of Mn.
 3. Welding materials for covered electrode arc welding according to claim 1 comprising on weight basis less than 1.5% of Si, less than 1.0% of Mn, 2 to 10% of CaF₂, 6 to 20% of CaCO₃, 0.3 to 2.0% of a mixture of MgO and TiO₂ and less than 1% of organic materials, the balance being Fe.
 4. Welding materials for carbon dioxide gas shielded arc welding according to claim 1 comprising on weight basis 0.1 to 0.5% of Si, 0.3 to 1.1% of Mn, 4 to 10% of CaF₂, 0.4 to 4% of CaCO₃, 0.6 to 2% of SiO₂, less than 2% of CaO and 2 to 6% of TiO₂, the balance being essentially Fe.
 5. Welding materials according to claim 1 comprising on weight basis less than 0.15% of Si, less than 0.35% of Mn, 4 to 5% of CaF₂ and 37.5 to 45.7% of a mixture of oxides having a basicity ranging from 1.7 to 6.3, the balance being essentially Fe.
 6. Welding materials according to claim 3 comprising on weight basis 0.8 to 1.4% of Si, less than 0.5% of Mn, 6.3 to 9% of CaF₂, 11.4 to 18% of CaCO₃, 1.2 to 1.65% of a mixture of MgO and TiO₂ and 0.75 to 0.9% of organic materials, the balance being essentially Fe.
 7. Welding materials according to claim 4 comprising on weight basis 0.1 to 0.43% of Si, 0.7 to 1.0% of Mn, 5.7 to 8.52% of CaF₂, 0.4 to 0.8% of CaCO₃, 0.8 to 1.4% of SiO₂ and 3.6 to 5% of TiO₂, the balance being essentially Fe. 